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\section{Introduction}

\PARstart{I}{n} the history of games, the implementation of audio has gone from the dedicated chip synthesis of the eighties to the triggering of high-quality pre-recorded samples of today \cite{collins2008gamesound}. Using a fixed pool of audio files ensures a certain level of fidelity and control, but leaves little room for adaptivity and variation, possibly resulting in listener fatigue. We wish to investigate methods that will increase the flexibility and expressiveness of audio in games as well as add new dimensions to game design.

Our approach is based on the idea of creating sounds from a \emph{source} and a \emph{descriptor}. Through synthesis, the source is mutated to fit the descriptor, resulting in a unique sound that has the properties of the descriptor while retaining some characteristics of the original source. This gives a potentially infinite amount of variations using a model with few parameters. Furthermore, the parameters of the descriptor can easily be coupled with other gameplay elements, for example the attributes of a character.

The source-descriptor model is well-suited to \emph{granular synthesis}, which is the technique used for this project. Granular synthesis is an method for audio synthesis based on the theories of Nobel Prize winner Dennis Gabor \cite{gabor1947hearing}. The basic idea of granular synthesis is to operate within the microstructure of an existing sound. The sound is partitioned into smaller chunks called grains, and these grains are then recombined and manipulated in various ways to create a whole new sound. This method has been used in many different contexts, from DSP effects (e.g. time stretching) to formalized composition \cite{xenakis1971formalized}.

Realizing that the sounds created with our model will be best suited for games with a non-realistic audio aesthetic, the scope has been limited to the specific subset of space weapon sounds. Our contribution is a system for procedural creation of such sounds called \emph{HDGrains} embedded in a simple 2D space shooter game as a proof of concept. We feel that this is a novel approach with potential for interesting and unexpected results.

In this report, we first give a general background of procedural audio in games to motivate our work in section \ref{background}. We consider the game design used in the demo and it's relation to procedural content generation in \ref{gamedesign}. Then we describe the method used in section \ref{method}. The results are presented in section \ref{results} and finally we examine the results and contemplate future work in section \ref{discussion}.